Flashing materials in the form of plate members or skirts are used in the manufacturing of sealed joints between building structures penetrating a roof surface, for example a sealed joint between the main frame of a window installed in a roof and the surrounding roofing, in particular as a skirt-shaped flashing at the lower horizontal member of the main frame.
Such materials have traditionally been constituted by lead plates of a thickness of approximately 1 mm. Lead as a flashing material has a number of advantages as it is very easy to plastically deform with only a very limited elasticity, i.e. the lead plate substantially stays in the form into which it is initially bend without any elastic bouncing back. This inherent feature of lead is of great advantage when a lead-skirt as part of an already attached flashing is shaped directly onto for example an undulated roof surface, in which case the skirt cannot be bend in excess in order to compensate for possible elastic re-bouncing.
Although lead for most purposes is almost non-elastic, there may be a minimal re-bouncing, however, as lead is a very heavy material, gravity alone will help the lead-skirt to be elastically bend into close contact with the roof surface. Further, the high density of lead and the corresponding high weight will also prevent the skirt from being bend backwards during storming weather.
Indeed, lead also has some very well known draw backs as it is environmentally harmful, due to its weight expensive to transport and handle and in some aspects difficult to apply, for example when joining together different lead elements. Further, lead may oxidise and subsequently leave streaky deposits on the surrounding roof surface.
In order to avoid the economical and environmental problems involved by the traditional use of lead in flashing materials, it has been suggested to manufacture flashings as sandwich constructions in which, typically, a stress damping and stabilizing core layer of ductile material is completely covered on one side by a foil sheeting. The core layer has typically been made out of polymeric material or bitumen product, and the foil has typically been a thin metal foil, preferably aluminium foil. Bitumen as a product class is normally adhesive at ambient temperatures which will assure that it will adhere to and stabilize the foil, however, when a non-adhering core material is used it may be necessary to coat the core material with a pressure-sensitive adhesive coating. Such flashing materials are disclosed in for example Danish Patent Specifications No. 148 064 and No. 145 509 as well as in German patent specification DE-A-4 032 058.
For use on roof surfaces in the form of undulated tiles with very deep troughs, the above discussed sandwich constructions has been developed further into wave-corrugated and pleated designs, in order to obtain a sufficiently manual deformability and stretchability to enable a good fit between the flashing and roofing.
However, even with these improved designs it has turned out to be difficult to obtain a close as well as a permanent fit between the flashing and the roof surface.
Correspondingly, flashings of the sandwich type has been proposed in which a further layer or structure has been embedded or added to the core layer, for example as an embedded metal mesh or grid as disclosed in for example GB-A-2 184 685 or WO 95/31620, as an embedded polymeric grid structure as in DE-U-298 04 503 or as an additional foil as in WO 99/13180. However, these constructions add considerably to the cost of manufacture and problems have also been encountered when the wire material of the metal meshes during the mounting procedures brake and subsequently penetrate the material in which they are embedded as well as the covering foil, this allowing water to enter.
GB-A-1 095 393 discloses an adhesive laminate, which may be used, for example, to provide a water and dustproof seal to joints in buildings. The laminate comprises a self-adhesive bituminous composition coated onto a flexible protective layer. The bituminous composition may contain a filler material, preferably comprising both fibrous and powdered filler. The powdered filler materials suggested are ground limestone silica and calcium carbonate surface-treated with stearic acid.
The lead-free flashing materials suggested in the prior art have had difficulty in gaining a footing in the market, as a competitive and equal alternative of lead flashings. Instead attempts encompassing efforts to improve traditional lead-flashings through wave pleated or folded designs, in which the lead thickness has been reduced, have been made to provide a good weather-proofness of the lead-flashing by painting or lacquering it.
Therefore, having regard to the above, it is the object of the present invention to provide an improved flashing material which has one or more of the above described desirable features of lead-flashings, i.e. being easy to bend with only very limited elastic-deformation properties as well as having a high density, and which is moreover easy and cheap in manufacture.